tests: add a NetworkCalls group for tests making network calls

Excluding this group can decrease the run time of tests during
development.

Signed-off-by: Kevin Decherf <kevin@kdecherf.com>

tests/Wallabag/CoreBundle/Controller/ConfigControllerTest.php

@@ -812,6 +812,9 @@ class ConfigControllerTest extends WallabagCoreTestCase
         $em->flush();
     }
 
+    /**
+     * @group NetworkCalls
+     */
     public function testDeleteAccount()
     {
         $client = $this->getClient();